A gas turbine operates by compressing air, combining the compressed air with fuel, igniting the mixture, and harnessing the expansion of the burning fuel to produce work. The exhaust stream in turn is utilized in part to assist the engine in perpetuating the cycle of compression, burning, and expansion. In a typical gas turbine engine, the compressor includes a set of spinning blade discs, sometimes referred to as compressor discs. Similarly, the portions of the engine after the combustion chamber, including the final stage, are comprised of one or more blade discs, sometimes referred to as turbine discs.
In order to maintain the various spinning blade discs of the gas turbine in a designed location within the engine housing, and in particular with respect to a close-fitting cylindrical air guide, structural supports are employed. These structural supports essentially bridge the engine housing to a central bearing for supporting the primary engine shaft. Because of the large volume of air and gases moving within the housing, and the high speeds at which such movement occurs, it is beneficial for the structural supports which extend into such airflow to be airfoil-shaped.
Such structural supports are typically constructed so as to withstand the relatively static stress imposed on them, e.g., compressive stress, torsional stress, buckling stress, etc. However, even when the structure exhibits adequate static strength in these areas, there are many vibrational excitations within a gas turbine engine, and these excitations can be transferred to the structural supports to induce additional stress. Moreover, if a modal response or resonance of a structural support is close in frequency to a substantial vibrational excitation of the engine, cumulative energy absorption occurs in the structural support resulting in sympathetic and potentially violent oscillations, leading to potential failure of the structural support.
However, due to impediments in the airflow within the engine, the vanes include several different airfoil shapes. The airfoil of a particular guide vane will depend upon where in the engine it is located relative to an impediment such as an engine mounting strut. For example, guide vanes directly upstream of the impediment may be shaped to modify and redirect the airflow more significantly than guide vanes that are not directly upstream of the impediment.
As noted above, the modal response of engine blades and vanes may be tuned to avoid certain high-energy frequency bands. However, unlike compressor and turbine blades which are largely identical, the wide variety of shapes for vanes increases the complexity of trying to tune each such element. Thus, the inventors have observed that a more efficient system is needed for allowing the frequency modes of vanes to be properly tuned.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as a reference to prior art, nor as an indication that any of the indicated problems were themselves appreciated in the art. While the principles described hereinafter may in some embodiments alleviate problems inherent in other systems, the scope of the protected innovation is defined by the attached claims, and not otherwise by the ability to solve any specific problem.